In the aircraft and aerospace industries, aluminum alloys are used extensively because of the durability of the alloys as well as the reduction in weight achieved by their use. Alloys useful in aircraft and aerospace applications must have excellent strength and toughness properties. A number of alloys have been developed for these applications. These types of alloys include wrought alloys that have been subjected to various heat treatment and deformation processes to optimize properties for a particular application. However, a continuing need remains in the industry for a high strength, high toughness aluminum alloy which may be useful in a variety of product applications where it may be difficult or inconvenient to apply cold deformation prior to subsequent heat treating processes such as artificial aging treatments. The present invention meets this need in the aircraft and aerospace industries by providing an aluminum alloy which contains critical amounts of copper, magnesium and, preferably, silver. The alloy of the present invention, as a result of the combination of alloying components, has potential applications in a wide variety of areas including forgings, plate, sheet, extrusions, weldable components and matrix material for composite structures.
Aluminum alloys are known in the art which contain magnesium, copper and silver.
Staley et al., in "Metallurgical Transactions", January, 1972, pages 191-199, discusses high strength Al-Zn-Mg-Cu alloys, with and without silver additions. In this publication, Staley et al. studied the effects of silver additions with respect to the heat treating characteristics of high strength alloys. Staley et al. makes reference to a publication by Polmear in "Journal of the Institute of Metals", 1960, Volume 89, pages 51 and 193, who reported that 0.3 to 1% of silver additions substantially increased the strength of Al-Zn-Mg-Cu alloys.
U.S. Pat. No. 3,414,406 to Doyle et al. discloses a copper, manganese and titanium-containing aluminum alloy with the inclusion of 0.1-0.5 weight percent of magnesium. The aluminum alloy also includes from 0.2-0.4 weight percent of silver. Moreover, the aluminum alloy of Doyle et al. requires an amount of silicon between 0.1 to 0.35 percent by weight.
U.S. Pat. No. 4,610,733 to Sanders et al. discloses a high strength, weldable aluminum base alloy characterized by high strength and designed for ballistics armor. The alloy includes 5-7 percent by weight copper and 0.1-0.3 percent by weight of magnesium. The alloy is subjected to processing conditions including cold work equivalent to 6 percent stretching and aging to achieve the desired product properties.
U.S. Pat. No. 4,772,342 to Polmear discloses a wrought aluminum-copper-magnesium-type aluminum alloy having copper in an amount between 5-7 percent by weight, magnesium in an amount between 0.3-0.8 percent by weight, silver in an amount between 0.2-1.0 percent by weight, along with manganese, zirconium, vanadium and the balance aluminum. In illustrated Example 2 of the Polmear patent, an alloy is disclosed containing 5.3 percent by weight of copper and 0.6 percent by weight of magnesium, such a composition exceeding the solubility limit of copper and magnesium in the alloy. Moreover, Polmear does not recognize obtaining the combination of high strength and toughness in these types of aluminum alloys as a result of limiting the amounts of copper and magnesium below the solubility limit.
The present invention is directed to an improved aluminum-copper-magnesium alloy, preferably with silver, having improved combinations of strength and toughness. The alloys of this invention have precise amounts of the alloying components as described herein and provide outstanding combinations of strength and toughness characteristics.